The present invention relates to fuel cells; more particularly, to supply air connections to fuel cell assemblies; and most particularly, to a system for automatically connecting and disconnecting an air supply to a fuel cell assembly in response to manifold air pressure.
Fuel cells which generate electric current by controllably combining elemental hydrogen and oxygen are well known. In one form of such a fuel cell, an anodic layer and a cathodic layer are separated by a permeable electrolyte formed of a ceramic solid oxide. Such a fuel cell is known in the art as a xe2x80x9csolid-oxide fuel cellxe2x80x9d (SOFC). Hydrogen, either pure or reformed from hydrocarbons, is flowed along the outer surface of the anode and diffuses into the anode. Oxygen, typically from air, is flowed along the outer surface of the cathode and diffuses into the cathode. Each O2 molecule is split and reduced to two O31 2 ions catalytically by the cathode. The oxygen ions diffuse through the electrolyte and combine at the anode/electrolyte interface with four hydrogen ions to form two molecules of water. The anode and the cathode are connected externally through the load to complete the circuit whereby four electrons are transferred from the anode to the cathode. When hydrogen is derived by xe2x80x9creformingxe2x80x9d hydrocarbons such as gasoline in the presence of limited oxygen, the xe2x80x9creformatexe2x80x9d gas includes CO which is converted to CO2 at the anode. Reformed gasoline is a commonly used fuel in automotive fuel cell applications.
A complete SOFC system typically includes auxiliary subsystems for, among other requirements, generating fuel by reforming hydrocarbons; tempering the reformate fuel and air entering the stack; providing air to the hydrocarbon reformer; providing air to the cathodes for reaction with hydrogen in the fuel cell stack; providing air for cooling the fuel cell stack; providing combustion air to an afterburner for unspent fuel exiting the stack; and providing cooling air to the afterburner and the stack.
In a solid-oxide fuel cell system, the xe2x80x9chotxe2x80x9d components, e.g., the fuel cell stacks, the fuel reformer, tail gas combuster, heat exchangers, and fuel/air manifold, are contained in a xe2x80x9chot zonexe2x80x9d within an insulative thermal enclosure. The thermal enclosure is intended specifically for minimizing heat transfer to its exterior and has no significant structural or protective function for its contents. A separate and larger structural enclosure surrounds the thermal enclosure, defining a xe2x80x9ccool zonexe2x80x9d outside the thermal enclosure for incorporation of xe2x80x9ccoolxe2x80x9d components, e.g., the air supply system and the electronic control system. The structural enclosure components are known in the art as a xe2x80x9cplant support modulexe2x80x9d (PSM).
Process air is directed to the fuel cell reformer and stacks typically via a manifold in the cool zone having a plurality of independently-controllable air valves for metering air as needed to a plurality of process locations and functions in the hot zone. The plenum is connected to the hot zone components via tubes, which tubes can become sufficiently hot to preclude use of low-cost materials such as rubber hoses. This condition pertains especially during shutdown of the fuel cell system when the tubes are not cooled by passage of incoming air through them. During normal operation of the system, there typically is sufficient active cooling of these tubes to permit use of low-cost materials.
Further, when the fuel cell system is in idle mode, it is desirable to retain high temperatures within the hot zone to permit rapid restart. The air supply tubes connected to the hot zone components are significant pathways for loss of heat by conduction.
What is needed is means for permitting use of low-cost materials such as rubber for air supply tubes connecting to the hot zone of an SOFC.
What is further needed is means for preventing loss of heat from the hot zone during idle mode by heat conduction through air supply tubes.
It is a principal object of the present invention to permit use of low-cost materials such as rubber for air supply tubes connecting to the hot zone of an SOFC.
It is a further object of the invention to prevent loss of heat from the hot zone during idle mode by heat conduction through air supply tubes.
Briefly described, air supply lines extending between a blower supply plenum to hot zone components of a solid-oxide fuel cell assembly are provided with means for automatically connecting the lines to, and retracting the lines from, the hot zone components. Each such hot zone component is provided with a socket, preferably hemispherical, for receiving a connector. Each such supply line comprises a connector having two concentric expandable bellows connected between the plenum and a nipple element having a central bore and nipple for mating with the socket. The inner bellows is coaxial with the socket and is connected to an individual supply port for the particular hot zone component. The outer bellows is connected to the main blower output. A return spring between the hot zone component and the nipple element urges the element from the socket, thereby disconnecting the supply line from the hot zone and breaking the conductive heat path when the blower is inoperative as during idle mode or shutdown. When the blower is re-energized, the outer bellows is pressurized and accordingly expands axially, overcoming the return spring, extending the inner bellows, and automatically urging the nipple element back into air-tight connection with the socket.